A gate electrode of a III-V compound HEMT (High Electron Mobility Transistor) semiconductor device mainly has a T-shaped structure. The conventional T-shaped gate electrode has an electrode structure in which a canopy part with a wide electrode width is formed on a leg part with a narrow electrode width.
The conventional T-shaped gate electrode is formed by sequentially laminating a titanium layer (Ti layer) as a Schottky electrode layer, a platinum layer (Pt layer) as a barrier layer, and a gold layer (Au layer) as a low-resistance layer. In particular, the canopy part is formed of the gold layer (Au layer) as a low-resistance layer.
However, since the barrier is laminated on the entire surface of the Schottky electrode layer, the barrier layer is exposed from the side surface of the leg part of the gate electrode. In addition, the Schottky electrode layer is generally thin. Therefore, the barrier layer, which is exposed from the side surface of the gate electrode formed, is in an adjacently contact state with respect to the semiconductor layer. Therefore, when a semiconductor device including a T-shaped gate electrode is operated, the barrier layer flows out to the semiconductor layer by heat during the operation, and the channel part right under the gate electrode is narrowed with a lapse of time. As a result, the drain to source current is decreased with a lapse of time. In other words, the life of the device is shortened.